Recently, liquid crystal display devices have been widely used as display devices of smartphones, personal assistant devices (PAD), tablet computers, car navigation systems and the like. In general, a liquid crystal display device comprises a liquid crystal display panel, and a flat lighting device (backlight device) overlaid on a back surface of the liquid crystal display panel to illuminate the liquid crystal display panel. A conventional backlight device comprises a reflective layer, a light guide, an optical sheet, LEDs serving as light sources, and a rectangular mold frame. The reflective layer, the light guide, and the optical sheet are mutually stacked and disposed in the mold frame. Peripheral portions of the reflective layer, the light guide, and the optical sheet are thereby supported and positioned by the mold frame.
Alternatively, there has been proposed a configuration wherein the mold frame is fitted in a case (backlight cover) formed of a metal plate and the reflective layer, the light guide, and the optical sheet are disposed in a cavity portion of the mold frame.
In recent years, as display areas have increased, there has been a continual demand for the frames of liquid crystal display devices to become ever narrower and the liquid crystal display devices to become ever thinner. However, the dimensions of the width, thickness, etc., of the mold frame in the above-described backlight unit is approaching the structural limit of injection molding.